In present magnetic storage media disk drives, magnetic media coating thicknesses and transducer fly heights are becoming progressively smaller as recording densities increase. Thus maintaining the enclosure, which houses the transducers and rotating media, free of particulate contamination becomes correspondingly more critical and the size particle that can be tolerated is much smaller. Of special concern are particles that might be generated having magnetic properties, since higher storage densities mean smaller magnetic domains exist on the recording surface, while most actuators for moving the head assembly contain strong permanent magnets.
It has become the practice to use an enclosure for the head-disk assembly that is sealed except for a breather that accommodates pressure differentials occasioned by conditions such as temperature change or atmospheric pressure variations. The filter system, to be effective, must quickly pick up particulate matter and effectively purge the entire working volume of the head-disk enclosure with frequent air changes. Disk drive assemblies, to be commercially competitive, must also meet a form factor limiting the overall dimensions.
There are, accordingly, conflicting objectives. Frequent air changes call for extended filter surfaces and large air flow paths to minimize resistance to circulation while not extending the physical dimensions of the drive. This is made more severe when an attempt is made to design half high drives that are only half the height of the normal form factor so that two drives can occupy the same space formerly occupied by a single drive.